Papadic Octoechos - "Parallage of John Koukouzeles": The four peripheral wheels for the Octoechos (top left: protos echoi; top right: devteros echoi; bottom left: tritos echoi; bottom right: tetartos echoi) and the tetraphonic tone system and its transpositions in the center—Koukouzelian wheel in an 18th-century manuscript (manuscript of the private collection by Demetrios Kontogiorges)